Spectroscopic studies of the corrosion of model iron electrodes in carbonate and phosphate buffer solutions (original) (raw)
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Raman spectroscopic studies of the corrosion of model iron electrodes in sodium chloride solution
Journal of Raman Spectroscopy, 2007
We have explored the un-enhanced Raman spectra of both single and twin electrodes in 3.5% NaCl solution (at ambient temperatures) over a range of applied potentials (between 20 and 200 mV) and times (between 0 and 5 h). Under these conditions, we observed the initial formation of 'green rust' (hydroxychlorides and/or hydroxycarbonates), followed by the formation of magnetite (Fe 3 O 4 ) and then a mixture of the a-and g-FeOOH (goethite and lepidocrocite, respectively). These data are consistent with a model for corrosion during which the initially formed magnetite is either covered, or replaced, by layers of the FeOOH oxidation products. Fitting of the data as a function of time and potential shows that, although the product range is independent of potential, the relative kinetics of formation of magnetite and its subsequent conversion to the g-FeOOH were potential and time dependent. Analysis by mapping of the dry corroded surface showed a variety of species, including green rust, some Fe(OH) 3 , as well as the g-FeOOH, and possibly some b-FeOOH. But no surface magnetite was found, indicating that this material had been either covered up or converted to FeOOH. We noted several complications during this work, including the interference of resonance effects (on the Raman intensities) and the heterogeneity of the corrosion process (and hence distribution of species on the corroded surface). However, we believe that the use of un-enhanced Raman methods has led to conclusions more likely to be relevant to 'real' corrosion processes.
Cement & Concrete Composites, 2002
Different electrochemical techniques (electrochemical impedance spectroscopy (EIS), ring-disk electrode, electrochemical quartz crystal microbalance (EQCM), and in situ Raman spectroscopy) have been employed to study the behaviour of the passive film formed on iron in alkaline medium simulating pore solution in fresh concrete. The study, based on low scan rate cyclic voltammetry performed over the entire electrolyte stability domain, allows for establishing the influence of the redox activity developing in the oxides layer on the electrochemical behaviour of the system and, thus, to get valuable information on the applicability of classical electrochemical techniques employed to assess corrosion of steel in concrete.
Electrochimica Acta, 1992
In situ" laser Raman spectra of the corrosion films on iron have been observed in aerated 5 M KOH and 0.15 M NaCl solutions via surface enhancement by the electrodeposition of a silver overlayer. Essentially the same spectra are observed in the two solutions as a function of applied potential in spite of a breakdown of passivity on iron in the chloride solution. FeJOH), and Fe,O, are found in the prepassive potential region while FeOOH is present in the passive region. A film which is very diilicult to reduce appears to be always present on the electrode surface even at hydrogen evolution potentials; this film is believed to be a-FeOOH. Surface enhanced Raman spectra of the corrosion films on chromium have also been obtained in NaCl solution for the first time. The passive film has a composition that corresponds most closely to an amorphous form of Cr,O, , with some Cr(OH), also present. The film is converted in the transpassive region to a higher oxide form, presumably CrO:-. Reversible reduction of this species to Cr,O, is indicated.
Electrochimica Acta, 2001
In situ surface enhanced Raman spectroscopy was employed to study the effect of dissolved oxygen (DO) on the composition of the corrosion film formed on a low carbon steel surface in 0.01 M NaCl solution. Raman spectra were taken during cyclic voltammetric and potential step experiments. The spectra taken during cyclic voltammetry were similar to those previously obtained for passive iron. It showed a peak for a trivalent species at 670 cm − 1 in the passive potential range, which was usually assigned to FeOOH rather than to g-Fe 2 O 3. However, in the spectra taken during potential step experiments, it was apparent that the main trivalent species in the corrosion film was g-Fe 2 O 3 at 640, 670, 715 cm − 1 , and DO behaved as an oxidizer to convert iron from the divalent state in Fe 3 O 4 to the trivalent state (g-Fe 2 O 3). The presence of g-Fe 2 O 3 in the corrosion film on iron was detected for the first time by taking SER spectra during potential step experiments. Though this film showed a weak protective property, and had corrosion products due to pitting induced by chloride ions, the detection of g-Fe 2 O 3 supports the previous ex situ and in situ findings that the trivalent oxide in iron passivity is g-Fe 2 O 3 .
Goethite (-FeOOH) and lepidocrocite (-FeOOH) are two common iron and steel corrosion products. The study of goethite and lepidocrocite is an interesting way to better understand the corrosion processes of iron and its behaviour in different environments. In this work the co-deposition of iron oxides and their transformation on inert subtracts were studied at room temperature. The films were obtained by electro-deposition using solutions containing Cl-, SO42- and Fe2+at different pH on platinum disks. Linear polarisation, amperommetry, electrochemical impedance and spectroscopy techniques were used in this study. Anodic polarisation curves showed a current shoulder at low anodic polarisation and a current peak at higher polarisation. The shoulder observed at low anodic polarisation corresponded to the formation of a precursor compound like Fe2+-Fe3+ hydrated oxide, which is later transformed to an oxy-hydroxide compounds. The electrodeposition of goethite and lepidocrocite occurs, firstly through formation of a green rust film, characterised by a shoulder in the polarisation curves, and subsequently through formation of an iron oxy-hydroxide film. The anion and the pH of the electrolyte played an important role in the formation and further transformation of the iron oxides compounds on the film. It was corroborated that the Cl- ions and high pH stimulated the green rust and final oxyhydroxide film formation, while the SO42- ions and low pH retarded the formation of these compounds.
Journal of Raman Spectroscopy, 2011
In several contexts such as cultural heritage, oil and gas or nuclear waste disposal, the long-term corrosion mechanisms of iron in anoxic soils are studied. For this purpose, corrosion layers formed on ferrous archaeological artefacts from the site of Glinet (16th century, Normandy, France) were characterised. The main phases identified are siderite (FeCO 3 ), chukanovite (iron hydroxycarbonate: Fe 2 (OH) 2 CO 3 and magnetite (Fe 3 O 4 ). In order to provide reliable Raman references for further studies on carbonated systems, the iron hydroxycarbonate (chukanovite) was synthesised on iron discs. The corrosion mechanisms were investigated by re-corroding the archaeological samples in a deuterated solution. Raman characterisation on cross sections inside the layer revealed the presence of deuterated chukanovite, allowing the deuterium tracing of the spreading of the corrosion. A set of chukanovite samples was synthesised with various D/H ratios. Using these reference data, the proportion of deuterated chukanovite in re-corroded artefacts was evaluated, and the corrosion rate was estimated as less than 1.6 µm/year.
Corrosion Science
The anticorrosive performance of zinc chromate and zinc phosphate, used as extracts in 0.1 M NaCl, was studied using electrochemical impedance spectroscopy (EIS), the scanning vibrating electrode technique (SVET) and open circuit potential (OCP) measurements. Neither of the pigments managed to totally prevent corrosion. Phosphate had a much lower inhibiting efficiency and acted at a very low rate, whereas chromate acted immediately after immersion, but lost some of its action after a few hours of continuous immersion. Iron corroded uniformly in the phosphate extract, whereas in the chromate extract nucleation of metastable pits occurred. Evolution of the chromate layer with time was revealed in the EIS spectra in the form of a relaxation constant that developed during immersion, which was interpreted as being due to the formation of a porous healing layer formed on repassivated pits. The joint use of open circuit potential measurements, EIS and SVET is illustrated as a means of assessing different phenomena on the metal surface.
Journal of Electroanalytical Chemistry and Interfacial Electrochemistry, 1987
The corrosion rate of a copper electrode in deaerated 1.0 M HCl by Fe(III) ions, in the absence and presence of benzotriaaole (BTAH), has been evaluated through weight-loss experiments using a rotating disk electrode (RDE). The corrosion process is controlled by transport of the Fe(III) ions to the electrode surface both in the absence and presence of BTAH. The inhibiting action is initiated at BTAH concentrations around 10 mM and the Langmuir adsorption isotherm is obeyed in the BTAH concentration range from 10 to 45 mM with an apparent equilibrium adsorption constant of 10 .M-'. Above this concentration, the Langmuir plot is not obeyed due to the formation of a multilayer. The surface films formed during the corrosion process have been investigated by "in situ" and "ex situ" fluorescence and Raman spectroscopy and characterized as being composed of the polymeric [Cu(I)BTA] complex and [Cu(I)ClBTAH],, the former as an inner layer response for the corrosion inhibition process.
Raman Studies of Corrosion Layers Formed on Archaeological Irons in Various Media
Journal of Nano Research, 8, 147-156., 2009
The description and identification of corrosion products formed on archaeological iron artefacts need various approaches at different observation scales. Among analytical techniques available to document phase structure at the microscopic range, Raman spectroscopy offers sensitivity and discrimination between iron corrosion products with an easy implementation. Results obtained for iron artefacts corrosion in soils and atmosphere are presented. Corrosion forms observed for anoxic and aerated soils on one hand and indoor atmosphere on the other are documented. Beyond the identification and organisation of corrosion products through hyperspectral imaging, Raman micro-spectroscopy could also provide quantitative phase proportions which will be needed in the proposition of reactivity diagnosis indicators.